The factory will produce nacelles for Siemens' D7 platform of offshore turbines, and is expected to begin operations by the middle of 2017.
The D7 platform consists of Siemens' 7MW turbine, unveiled at the EWEA Offshore conference in Copenhagen in March. It is an uprated version of the 6MW turbine already in series production. A 7MW prototype was installed in Denmark in May.
The new facility is located at the harbour's edge so components can be loaded directly on to transport vessels. It will cover 170 square kilometres.
An official signing ceremony between Siemens and Cuxhaven Harbour will take place on 13 August, with a ground breaking event planned for later this year.
Siemens president and CEO Joe Kaeser said "The new Siemens factory will employ up to 1,000 skilled employees. The expansion of offshore wind power capacity in Germany and Europe represents an enormous opportunity for northern Germany and Siemens."
The firm is also building a blade factory and turbine assembly hub at the Green Port Hull site, northeast England. It is also expected to reach full operational capacity by 2017, Siemens said.